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While starting my transition to an IPv6-enabled network, I discovered
that rpc.lockd was failing to start on my systems.
It seems that rpc.lockd insists on using IPv6 if it is available in the
kernel, whether or not IPv6 is enabled in /etc/netconfig
The attached patch adds options to rpc.lockd
-4 Use IPv4 only, whether IPv6 is available or not
-6 Use both IPv4 and IPv6 if IPv6 is available; silently
use IPv4 only if IPv6 is not available (default)
Any objections or comments?

This changes the semantics that have been traditional for these options.
(sshd, named, etc.)
-4 forces only ipv4
-6 forces only ipv6
these flags are mutually exclusive.
absence of both means use what's available.
I think we should make rpc.lockd behave the same way.

So, for consistency with nfsd, should we modify lockd to only listen on
IPv4 by default, and require explicit option to listen on IPv6?